Brachyspira hyodysenteriae is an anaerobic, oxygen tolerant, Gram-negative spirochete that is strongly β-hemolytic. In the past, Brachyspira hyodysenteriae was also known as Treponema hyodysenteriae and Serpulina hyodysenteriae. It is the etiological agent of swine dysentery, a mucohemorrhagic diarrheal disease of post-weaning pigs. Infection in swine with this bacterium can be suppressed with antimicrobials. However, recent restrictions on the use of antibiotics in animal feed provide impetus for the identification of candidate vaccine antigens as alternatives to the use of antimicrobials.
Swine dysentery (SD) is a mucohemorrhagic diarrheal disease of post-weaning pigs. SD has a major economic impact worldwide. The severity of the symptoms is variable between individuals and herds. The first signs of infection include soft, yellow to gray faeces, loss of appetite and increased rectal temperature in some animals. Subsequent to this, the faeces begin to contain flecks of blood and plugs of mucus. As the disease progresses, the faeces become watery, and prolonged diarrhea may lead to death by dehydration. Faeces containing B. hyodysenteriae are ingested by susceptible pigs, after which the organisms survive passage through the acidic conditions of the stomach and reach the large intestine. Experimental evidence suggests that the organism has a chemotactic response to mucus, enabling it to navigate to the colon mucosa where it invades the colon crypts. The large intestine is the major site for water and electrolyte resorption in pigs; damage to the large intestine thus results in colon absorption failure and dehydration.
Diagnosis of SD is based on clinical signs, herd history and isolation of B. hyodysenteriae on selective medium. B. hyodysenteriae is often difficult to isolate because of its slow growth and anaerobic requirements, a problem exacerbated by poor storage and transportation of samples. Even when isolation is possible, biochemical tests of isolates are unable to differentiate between B. hyodysenteriae and B. innocens, a non-pathogenic intestinal spirochete. The costly and time consuming nature of enter pathogenic studies in pigs or suitable animal models (such as mice, guinea pigs and chickens) precludes this approach for regular diagnosis.
Several virulence factors of B. hyodysenteriae have been identified and their role in the pathogenesis of swine dysentery investigated. For example, the initial colonization of the colon by B. hyodysenteriae is facilitated by its chemotactic response to mucus. (Kennedy, M. J., D. K. Rosnick, R. G. Ulrich, and R. J. Yancey. 1988, J. Gen. Microbiol. 134: 1565-1576). (Kennedy, M. J., and R. J. Yancey. 1996, Vet. Microbiol. 49: 21-30).
The importance of chemotaxis was demonstrated by Rosey, (Rosey, E. L., M. J. Kennedy, and R. J. Yancey, Jr. 1996, Infect. Immun. 64: 4154-4162), who showed that a dual flagella mutant was severely attenuated in a murine model. Once the colonization of the swine caecum is established, NADH oxidase is thought to protect the Brachyspira from oxygen toxicity. (Stanton, T. B., and N. S. Jensen. 1993, J. Bacteriol. 175: 2980-2987). (Stanton, T. B., and R. Sellwood. 1999, Anaerobe 5: 539-546). This hypothesis is supported by the observation that an NADH oxidase mutant exhibited reduced colonization of the swine caecum. The caecal lesions apparent on pathological examination of chronically infected swine can be induced by administration of B. hyodysenteriae haemolysin-containing extracts. Initially, three distinct putative haemolysin genes, tlyA, tlyB and tlyC were cloned and sequenced. (Muir, S., M. B. Koopman, S. J. Libby, L. A. Joens, F. Heffron, and J. G. Kusters. 1992, Infect. Immun. 60: 529-535). (ter Huume, A. A., S. Muir, M. van Houten, B. A. van der Zeijst, W. Gaastra, and J. G. Kusters. 1994, Microb. Pathog. 16: 269-282). A recent report by Hsu et al. has cast doubt on whether the tly genes actually encode haemolysins and has implicated another gene hlyA in haemolysin production (Hsu, T., D. L. Hutto, F. C. Minion, R. L. Zuerner, and M. J. Wannemuehler. 2001, Infect. Immun. 69: 706-711).
In the search for antigens which elicit a protective immune response, several proteins have been identified which localize to the outer membrane of B. hyodysenteriae. A Proteinase K sensitive 16-kDa antigen was localized to the outer membrane, Subsequently the gene encoding this antigen, smpA; was cloned and found not to be expressed in vivo (Thomas, W., R. Sellwood, and R. J. Lysons. 1992, Infect. Immun. 60: 3111-3116). (Sellwood, R., F. Walton, W. Thomas, M. R. Burrows, and J. Chesham. 1995, Vet. Microbiol. 44: 25-35). An extracytoplasmic 39-kDa antigen, Vsp39, was identified by surface iodination as the predominant surface component of B. hyodysenteriae (Gabe, J. D., R. E. Chang, R. J. Slomiany, W. H. Andrews, and M. T. Mccaman. 1995, Infect. Immun. 63: 142-148). While the gene encoding Vsp39 has not been cloned, a series of related tandem paralogous genes encoding 39-kDa proteins with 83-90% identity was identified (Gabe, J. D., E. Dragon, R. J. Chang, and M. T. McCaman. 1998, Identification of a linked set of genes in Serpulina hyodysenteriae (B204) predicted to encode closely related 39-kilodalton extracytoplasmic proteins. J. Bacteriol. 180: 444-448). (McCaman, M. T., K. Auer, W. Foley, and J. D. Gabe. 1999, Vet. Microbiol. 68: 273-283). A putative 30-kDa lipoprotein, BmpB, was found to react with convalescent pig sera. No further data of this protein have been published however (Lee, B. J., T. La, A. S. Mikosza, and D. J. Hampson. 2000, Vet. Microbiol. 76: 245-257).
It is therefore clear that there is a need for new and effective vaccines, especially vaccines that provide broad protection.
It is an objective of the present invention to provide novel vaccines for combating